Salawat: The Heaviest Deed in the Scale

Hawzah News Agency- Imam Baqir or Imam Sadiq(pbut) said:

عَنْ أَحَدِهِمَا عَلَيْهِمَا اَلسَّلاَمُ قَالَ: مَا فِي اَلْمِيزَانِ شَيْءٌ أَثْقَلَ مِنَ اَلصَّلاَةِ عَلَى مُحَمَّدٍ وَ آلِ مُحَمَّدٍ وَ إِنَّ اَلرَّجُلَ لَتُوضَعُ أَعْمَالُهُ فِي اَلْمِيزَانِ فَتَمِيلُ بِهِ فَيُخْرِجُ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ اَلصَّلاَةَ عَلَيْهِ فَيَضَعُهَا فِي مِيزَانِهِ فَيَرْجَحُ بِهِ .

Nothing is heavier in the scale (on the Day of Judgment) than sending blessings (salawat) upon Muhammad and the progeny of Muhammad.
Indeed, a man’s deeds may be placed on the scale and it leans against him, then the Prophet (pbuh) brings forth the salawat that he had sent upon him, places it upon his scale — and it outweighs (in his favor).

Usul al-Kafi, Vol. 2, p. 494, No. 15